[clang][CodeGen] Fix sub-optimal clang CodeGen for __atomic_test_and_set (#160098)

Clang CodeGen for `__atomic_test_and_set` would emit a `store`
instruction that stores an `i1` value:

```cpp
bool f(void *ptr) {
  return __atomic_test_and_set(ptr, __ATOMIC_RELAXED);
}
```

```llvm
%1 = atomicrmw xchg ptr %0, i8 1 monotonic, align 1
%tobool = icmp ne i8 %1, 0
store i1 %tobool, ptr %atomic-temp, align 1
```

which could lead to suboptimal binary code, for example on x86_64:

```asm
f:
    mov     al, 1
    xchg    byte ptr [rdi], al
    test    al, al
    setne   al
    setne   byte ptr [rsp - 1]
    ret
```

The last `setne` instruction is obviously redundant. This patch fixes
this issue by first zero-extending `%tobool` to an `i8` before the
store. This effectively eliminates the last `setne` instruction in the
binary code sequence. The `test` and `setne` on `al` is kept still,
though.

-----

I'm quite conservative about the codegen in this patch. Vanilla gcc
actually emits simpler code for `__atomic_test_and_set`:

```cpp
bool f(void *ptr) {
  return __atomic_test_and_set(ptr, __ATOMIC_RELAXED);
}
```

```asm
f:
    mov     eax, 1
    xchg    al, BYTE PTR [rdi]
    ret
```

It seems like gcc assumes `ptr` would always point to a valid `bool`
value as required by the ABI. I'm not sure if we should also make this
assumption.

Related to #121943 .

Author: Lancern

clang/lib/CodeGen/CGAtomic.cpp

@@ -734,7 +734,8 @@ static void EmitAtomicOp(CodeGenFunction &CGF, AtomicExpr *E, Address Dest,
         CGF.emitAtomicRMWInst(llvm::AtomicRMWInst::Xchg, Ptr,
                               CGF.Builder.getInt8(1), Order, Scope, E);
     RMWI->setVolatile(E->isVolatile());
-    llvm::Value *Result = CGF.Builder.CreateIsNotNull(RMWI, "tobool");
+    llvm::Value *Result = CGF.EmitToMemory(
+        CGF.Builder.CreateIsNotNull(RMWI, "tobool"), E->getType());
     auto *I = CGF.Builder.CreateStore(Result, Dest);
     CGF.addInstToCurrentSourceAtom(I, Result);
     return;

clang/test/CodeGen/atomic-test-and-set.c

@@ -81,7 +81,8 @@ void clear_dynamic(char *ptr, int order) {
 // CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[PTR_ADDR]], align 8
 // CHECK-NEXT:    [[TMP1:%.*]] = atomicrmw xchg ptr [[TMP0]], i8 1 monotonic, align 1
 // CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i8 [[TMP1]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT:%.*]] = zext i1 [[TOBOOL]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[TMP2:%.*]] = load i8, ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[LOADEDV:%.*]] = trunc i8 [[TMP2]] to i1
 // CHECK-NEXT:    ret void
@@ -99,7 +100,8 @@ void test_and_set_relaxed(char *ptr) {
 // CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[PTR_ADDR]], align 8
 // CHECK-NEXT:    [[TMP1:%.*]] = atomicrmw xchg ptr [[TMP0]], i8 1 acquire, align 1
 // CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i8 [[TMP1]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT:%.*]] = zext i1 [[TOBOOL]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[TMP2:%.*]] = load i8, ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[LOADEDV:%.*]] = trunc i8 [[TMP2]] to i1
 // CHECK-NEXT:    ret void
@@ -117,7 +119,8 @@ void test_and_set_consume(char *ptr) {
 // CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[PTR_ADDR]], align 8
 // CHECK-NEXT:    [[TMP1:%.*]] = atomicrmw xchg ptr [[TMP0]], i8 1 acquire, align 1
 // CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i8 [[TMP1]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT:%.*]] = zext i1 [[TOBOOL]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[TMP2:%.*]] = load i8, ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[LOADEDV:%.*]] = trunc i8 [[TMP2]] to i1
 // CHECK-NEXT:    ret void
@@ -135,7 +138,8 @@ void test_and_set_acquire(char *ptr) {
 // CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[PTR_ADDR]], align 8
 // CHECK-NEXT:    [[TMP1:%.*]] = atomicrmw xchg ptr [[TMP0]], i8 1 release, align 1
 // CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i8 [[TMP1]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT:%.*]] = zext i1 [[TOBOOL]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[TMP2:%.*]] = load i8, ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[LOADEDV:%.*]] = trunc i8 [[TMP2]] to i1
 // CHECK-NEXT:    ret void
@@ -153,7 +157,8 @@ void test_and_set_release(char *ptr) {
 // CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[PTR_ADDR]], align 8
 // CHECK-NEXT:    [[TMP1:%.*]] = atomicrmw xchg ptr [[TMP0]], i8 1 acq_rel, align 1
 // CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i8 [[TMP1]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT:%.*]] = zext i1 [[TOBOOL]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[TMP2:%.*]] = load i8, ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[LOADEDV:%.*]] = trunc i8 [[TMP2]] to i1
 // CHECK-NEXT:    ret void
@@ -171,7 +176,8 @@ void test_and_set_acq_rel(char *ptr) {
 // CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[PTR_ADDR]], align 8
 // CHECK-NEXT:    [[TMP1:%.*]] = atomicrmw xchg ptr [[TMP0]], i8 1 seq_cst, align 1
 // CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i8 [[TMP1]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT:%.*]] = zext i1 [[TOBOOL]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[TMP2:%.*]] = load i8, ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[LOADEDV:%.*]] = trunc i8 [[TMP2]] to i1
 // CHECK-NEXT:    ret void
@@ -200,27 +206,32 @@ void test_and_set_seq_cst(char *ptr) {
 // CHECK:       [[MONOTONIC]]:
 // CHECK-NEXT:    [[TMP2:%.*]] = atomicrmw xchg ptr [[TMP0]], i8 1 monotonic, align 1
 // CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i8 [[TMP2]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT:%.*]] = zext i1 [[TOBOOL]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    br label %[[ATOMIC_CONTINUE:.*]]
 // CHECK:       [[ACQUIRE]]:
 // CHECK-NEXT:    [[TMP3:%.*]] = atomicrmw xchg ptr [[TMP0]], i8 1 acquire, align 1
 // CHECK-NEXT:    [[TOBOOL1:%.*]] = icmp ne i8 [[TMP3]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL1]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT1:%.*]] = zext i1 [[TOBOOL1]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT1]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    br label %[[ATOMIC_CONTINUE]]
 // CHECK:       [[RELEASE]]:
 // CHECK-NEXT:    [[TMP4:%.*]] = atomicrmw xchg ptr [[TMP0]], i8 1 release, align 1
 // CHECK-NEXT:    [[TOBOOL2:%.*]] = icmp ne i8 [[TMP4]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL2]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT2:%.*]] = zext i1 [[TOBOOL2]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT2]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    br label %[[ATOMIC_CONTINUE]]
 // CHECK:       [[ACQREL]]:
 // CHECK-NEXT:    [[TMP5:%.*]] = atomicrmw xchg ptr [[TMP0]], i8 1 acq_rel, align 1
 // CHECK-NEXT:    [[TOBOOL3:%.*]] = icmp ne i8 [[TMP5]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL3]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT3:%.*]] = zext i1 [[TOBOOL3]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT3]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    br label %[[ATOMIC_CONTINUE]]
 // CHECK:       [[SEQCST]]:
 // CHECK-NEXT:    [[TMP6:%.*]] = atomicrmw xchg ptr [[TMP0]], i8 1 seq_cst, align 1
 // CHECK-NEXT:    [[TOBOOL4:%.*]] = icmp ne i8 [[TMP6]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL4]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT4:%.*]] = zext i1 [[TOBOOL4]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT4]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    br label %[[ATOMIC_CONTINUE]]
 // CHECK:       [[ATOMIC_CONTINUE]]:
 // CHECK-NEXT:    [[TMP7:%.*]] = load i8, ptr [[ATOMIC_TEMP]], align 1
@@ -239,7 +250,8 @@ void test_and_set_dynamic(char *ptr, int order) {
 // CHECK-NEXT:    [[ARRAYDECAY:%.*]] = getelementptr inbounds [10 x i32], ptr [[X]], i64 0, i64 0
 // CHECK-NEXT:    [[TMP0:%.*]] = atomicrmw volatile xchg ptr [[ARRAYDECAY]], i8 1 seq_cst, align 4
 // CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i8 [[TMP0]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT:%.*]] = zext i1 [[TOBOOL]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[TMP1:%.*]] = load i8, ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[LOADEDV:%.*]] = trunc i8 [[TMP1]] to i1
 // CHECK-NEXT:    ret void
@@ -301,7 +313,8 @@ void clear_incomplete(struct incomplete *ptr) {
 // CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[PTR_ADDR]], align 8
 // CHECK-NEXT:    [[TMP1:%.*]] = atomicrmw xchg ptr [[TMP0]], i8 1 monotonic, align 4
 // CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i8 [[TMP1]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT:%.*]] = zext i1 [[TOBOOL]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[TMP2:%.*]] = load i8, ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[LOADEDV:%.*]] = trunc i8 [[TMP2]] to i1
 // CHECK-NEXT:    ret void
@@ -318,7 +331,8 @@ void test_and_set_int(int *ptr) {
 // CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[PTR_ADDR]], align 8
 // CHECK-NEXT:    [[TMP1:%.*]] = atomicrmw xchg ptr [[TMP0]], i8 1 monotonic, align 1
 // CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i8 [[TMP1]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT:%.*]] = zext i1 [[TOBOOL]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[TMP2:%.*]] = load i8, ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[LOADEDV:%.*]] = trunc i8 [[TMP2]] to i1
 // CHECK-NEXT:    ret void
@@ -335,7 +349,8 @@ void test_and_set_void(void *ptr) {
 // CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[PTR_ADDR]], align 8
 // CHECK-NEXT:    [[TMP1:%.*]] = atomicrmw xchg ptr [[TMP0]], i8 1 monotonic, align 1
 // CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i8 [[TMP1]], 0
-// CHECK-NEXT:    store i1 [[TOBOOL]], ptr [[ATOMIC_TEMP]], align 1
+// CHECK-NEXT:    [[TOBOOL_ZEXT:%.*]] = zext i1 [[TOBOOL]] to i8
+// CHECK-NEXT:    store i8 [[TOBOOL_ZEXT]], ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[TMP2:%.*]] = load i8, ptr [[ATOMIC_TEMP]], align 1
 // CHECK-NEXT:    [[LOADEDV:%.*]] = trunc i8 [[TMP2]] to i1
 // CHECK-NEXT:    ret void